1. Field of the Invention
The present invention relates to a radio communication apparatus and, particularly, to a radio communication apparatus including a first antenna and a second antenna.
2. Description of Related Art
A method of processing signals in different frequency bands with use of two antennas is disclosed (United States Patent Publication No. 2005/0054383). In this method, signals of 5 GHz and 2.4 GHz are detected using two antennas. Then, which of the signals from the two antennas is to be used is determined according to a control signal. Further, the signals of 2.4 GHz and 5 GHz are divided by a diplexer (branching circuit with filter). The control signal is supplied from a baseband processor including an OFDM processor to a switch placed between the antennas and the diplexer.
As a technique related thereto, a communication apparatus that performs transmission and reception using a plurality of antennas is disclosed (Japanese Unexamined Patent Publication No. 10-210099). The communication apparatus includes a branching circuit that divides a high-frequency signal into several carrier frequencies. The communication apparatus then collects the signal divided by the branching circuit and demodulates it.
The configuration of the communication apparatus disclosed in Japanese Unexamined Patent Publication No. 10-210099 is described hereinafter with reference to FIG. 8. FIG. 8 is a block diagram showing the apparatus configuration disclosed in Japanese Unexamined Patent Publication No. 10-210099 in a simplified form. Referring to FIG. 8, a first antenna 71 is connected to a switch 75 through a first transmission line 73. Further, a second antenna 72 is connected to the switch 75 through a second transmission line 74. The first antenna 71 and the second antenna 72 are dual-band antennas. A control signal from a control circuit 76 is input to the switch 75. The antenna to be used by the switch 75 is switched according to the control signal.
A received signal from the switch 75 is input to a first transmitting/receiving circuit 77 or a second transmitting/receiving circuit 78. The first transmitting/receiving circuit 77 is a circuit for 2.4 GHz signals, and the second transmitting/receiving circuit 78 is a circuit for 5 GHz signals. The first transmitting/receiving circuit 77 and the second transmitting/receiving circuit 78 are configured by a baseband processor, an RF circuit that converts an RF signal into a baseband signal and connects it to the baseband processor, and so on. In this example, one of the first antenna 71 and the second antenna 72 is selected by the switch 75. The switching of the antenna is performed according to the power level of the received signal. The antenna with a higher power level is selected.